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Rear brake seems warped.

Started by d0n, September 01, 2021, 01:45:36 PM

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My new radrunner plus rear brake disc feels warped. When applying the rear brake... without changing the pressure on the brake lever, the bike slows but it surges and slows, surges and slows and on and on. It's like the brakes catch harder in one area of the disc and then less and then back to harder and so on. Very annoying.

Is there a fix for this?


When something like that happened to my front disk, I assumed I'd contaminated it by touching it inadvertently. IIRC, I fixed it by spraying a little contact cleaner on a paper towel and wiping the disk.

Radding Along

The rear brake rotor is warped, not the pads. Have someone hold the handlebars while pulling the bike up on the kickstand a little. Essentially you are trying to spin the back wheel freely.

Move the rear wheel slowly to see where it catches on the pad. Note which side of the pad it is touching. If you can't see it well, put something white on the ground to create a light background for you to view it better.

Once you locate a spot, use an adjustable wrench on the rotor to bend it whichever way it needs to go. You should be able to get the warp out if you do things correctly.

If you can't fix it, call Rad and have them send a new rear rotor. They are very easy to replace.

Radding Along

Sorry, forgot you had a center stand. No need for a second person. Put it on the center stand and straighten out the rotor.

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